Investment Securities, at Fair Value - Scheduled Maturity of CMBS (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value
Total	$ 40,974	$ 47,215
CMBS [Member]
Amortized Cost
Due within one year	0
Due after one year through five years	17,895
Due after five years through 10 years	12,053
Due after 10 years	13,058
Amortized Cost	43,006	48,297
Fair Value
Due within one year	0
Due after one year through five years	18,445
Due after five years through 10 years	9,156
Due after 10 years	13,373
Total	$ 40,974	$ 47,215